As the news of Michael Jackson's death spread around the world on June 25, the social-networking site Twitter came to a virtual standstill, flooded with visitors tweeting the news. Within moments of the first breaking news reports  indicating that Jackson had suffered cardiac arrest and had been rushed via ambulance to a Los Angeles hospital  both #michaeljackson and cardiac arrest emerged as two of the network's highest-rated "trending topics." As TIME's Michael Scherer notes, nearly three times as many tweets were posted about Michael Jackson on Thursday than about either Iran or swine flu. (See TIME's Michael Jackson tribute: "The Talent and the Tragedy.")

In the hour following confirmation of his death, celebrities rushed to make their grief and condolences public:

MC Hammer (MCHammer):
I have no words.. I loved Michael Jackson.. RIP... I will be mourning my friend , brother, mentor and inspiration.. He gave me and my family hope. I would never have been me without him.

Lance Armstrong (lancearmstrong):
Terrible news about Michael Jackson and Farah Fawcett. My best to their friends, fans, and families.

Danica Patrick (DanicaPatrick):
I can not believe Michael Jackson and Farrah passed away. Rest in peace.

Wyclef Jean (wyclefjean):
Michael Jackson was my music god, he made me believe that all things are possible and through positive music he will live forever...

Alyssa Milano (Alyssa_Milano):
Remember the first time you saw him moonwalk? RIP Michael Jackson

Lindsay Lohan:
NO OMG ... sending my love and prayers out to Michael and his family ... i feel sick..

Josh Groban (joshgroban):
Definitely a "Where were you when..." day. Lost a great artist who had great demons.

Britney Spears (britneyspears):
He was a wonderful man and will be greatly missed.

Ashley Tisdale (ashleytisdale):
I have to say, the 6 of us from HSM were very lucky to have met such an amazing man. I will remember that moment forever. RIP Michael

Stephanie Pratt (stephaniepratt):
"Wow Sad day Remembering how much you loved the thriller video when u were 2 yrs.old  Must have watched u dance 2 it a million times" - My mama just texted me that :(

Meghan McCain (McCainBlogette):
prayers go out to the King of Pop's family, a sombre day...

Jane Fonda (Janefonda):
I am stunned. My friend, Michael Jackson is dead. He lived with me for a week on "Golden Pond" set after "Thriller."

Ellen DeGeneres (TheEllenShow):
So sad to hear about Michael Jackson. His music changed our lives. The world has lost an amazing singer and dancer. I will miss him.

Sean (Diddy) Combs (iamdiddy):
Michael Jackson showed me that you can actually see the beat. He made the music come to life!! He made me believe in magic. I will miss him!